STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

Portions of this work were funded by Subcontract No. ZCO-0-30017-01 with the National Renewable Energy Laboratory under Prime Contract No. DE-AC36-99GO10337 with the U.S. Department of Energy. Accordingly, the United States Government may have certain rights in this invention.

FIELD OF THE INVENTION

The present invention relates to variant cellobiohydrolase enzymes and isolated nucleic acid sequences which encode polypeptides having cellobiohydrolase activity. The invention also relates to nucleic acid constructs, vectors, and host cells comprising the nucleic acid sequences as well as methods for producing recombinant variant CBH polypeptides.

BACKGROUND OF THE INVENTION

Cellulose and hemicellulose are the most abundant plant materials produced by photosynthesis. They can be degraded and used as an energy source by numerous microorganisms, including bacteria, yeast and fungi, that produce extracellular enzymes capable of hydrolysis of the polymeric substrates to monomeric sugars (Aro et al., J. Biol. Chem., vol. 276, no. 26, pp. 24309-24314, Jun. 29, 2001). As the limits of non-renewable resources approach, the potential of cellulose to become a major renewable energy resource is enormous (Krishna et al., Bioresource Tech. 77:193-196, 2001). The effective utilization of cellulose through biological processes is one approach to overcoming the shortage of foods, feeds, and fuels (Ohmiya et al., Biotechnol. Gen. Engineer. Rev. vol. 14, pp. 365-414, 1997).

Cellulases are known to be produced by a large number of bacteria, yeast and fungi. Certain fungi produce a complete cellulase system capable of degrading crystalline forms of cellulose, such that the cellulases are readily produced in large quantities via fermentation. Filamentous fungi play a special role since many yeast, such as Saccharomyces cerevisiae, lack the ability to hydrolyze cellulose. See, e.g., Aro et al., 2001; Aubert et al., 1988; Wood et al., Methods in Enzymology, vol. 160, no. 9, pp. 87-116, 1988, and Coughlan, et al., “Comparative Biochemistry of Fungal and Bacterial Cellulolytic Enzyme Systems” Biochemistry and Genetics of Cellulose Degradation, pp. 11-30 1988.

The fungal cellulase classifications of CBH, EG and BG can be further expanded to include multiple components within each classification. For example, multiple CBHs, EGs and BGs have been isolated from a variety of fungal sources including Trichoderma reesei which contains known genes for 2 CBHs, i.e., CBH I and CBH II, at least 8 EGs, i.e., EG I, EG II, EG III, EGIV, EGV, EGVI, EGVII and EGVIII, and at least 5 BGs, i.e., BG1, BG2, BG3, BG4 and BGS.

In order to efficiently convert crystalline cellulose to glucose the complete cellulase system comprising components from each of the CBH, EG and BG classifications is required, with isolated components less effective in hydrolyzing crystalline cellulose (Filho et al., Can. J. Microbiol. 42:1-5, 1996). A synergistic relationship has been observed between cellulase components from different classifications. In particular, the EG-type cellulases and CBH-type cellulases synergistically interact to more efficiently degrade cellulose. See, e.g., Wood, Biochemical Society Transactions, 611th Meeting, Galway, vol. 13, pp. 407-410, 1985.

Cellulases are known in the art to be useful in the treatment of textiles for the purposes of enhancing the cleaning ability of detergent compositions, for use as a softening agent, for improving the feel and appearance of cotton fabrics, and the like (Kumar et al., Textile Chemist and Colorist, 29:37-42, 1997).

Hence, cellulases produced in fungi and bacteria have received significant attention. In particular, fermentation of Trichoderma spp. (e.g., Trichoderma longibrachiatum or Trichoderma reesei) has been shown to produce a complete cellulase system capable of degrading crystalline forms of cellulose.

Although cellulase compositions have been previously described, there remains a need for new and improved cellulase compositions for use in household detergents, stonewashing compositions or laundry detergents, etc. Cellulases that exhibit improved performance are of particular interest.

BRIEF

SUMMARY

OF THE INVENTION

In one embodiment the invention is directed to a variant CBH I cellulase, wherein said variant comprises a substitution or deletion at a position corresponding to one or more of residues S8, Q17, G22, T41, N49, S57, N64, A68, A77, N89, S92, N103, A112, S113, E193, S196, M213, L225, T226, P227, T246, D249, R251, Y252, T255, D257, D259, S278, S279, K286, L288, E295, T296, S297, A299, N301, E325, T332, F338, S342, F352, T356, Y371, T380, Y381, V393, R394, S398, V403, S411, G430, G440, T445, T462, T484, Q487, and P491 in CBH I from Hypocrea jecorina (SEQ ID NO: 2). In first aspect, the invention encompasses an isolated nucleic acid encoding a polypeptide having cellobiohydrolase activity, which polypeptide is a variant of a glycosyl hydrolase of family 7, and wherein said nucleic acid encodes a substitution at a residue which is sensitive to temperature stress in the polypeptide encoded by said nucleic acid, wherein said variant cellobiohydrolase is derived from H. jecorina cellobiohydrolase. In second aspect, the invention encompasses an isolated nucleic acid encoding a polypeptide having cellobiohydrolase activity, which polypeptide is a variant of a glycosyl hydrolase of family 7, and wherein said nucleic acid encodes a substitution at a residue which is effects enzyme processitivity in the polypeptide encoded by said nucleic acid, wherein said variant cellobiohydrolase is derived from H. jecorina cellobiohydrolase. In third aspect, the invention encompasses an isolated nucleic acid encoding a polypeptide having cellobiohydrolase activity, which polypeptide is a variant of a glycosyl hydrolase of family 7, and wherein said nucleic acid encodes a substitution at a residue which is effects product inhibition in the polypeptide encoded by said nucleic acid, wherein said variant cellobiohydrolase is derived from H. jecorina cellobiohydrolase.

In a second embodiment the invention is directed to a variant CBH I cellulose comprising a substitution at a position corresponding to one or more of residues S8P, Q17L, G22D, T41I, N49S, S57N, N64D, A68T, A77D, N89D, S92T, N103I, A112E, S113(T/N/D), E193V, S196T, M213I, L225F, T226A, P227(L/T/A), T246(C/A), D249K, R251A, Y252(A/Q), T255P, D257E, D259W, S278P, S279N, K286M, L288F, E295K, T296P, S297T, A299E, N301(R/K), E325K, T332(K/Y/H), F338Y, S342Y, F352L, T356L, Y371C, T380G, Y381D, V393G, R394A, S398T, V403D, S411F, G430F, G440R, T462I, T484S, Q487L and/or P491L in CBH I from Hypocrea jecorina (SEQ ID NO: 2). In one aspect of this embodiment the variant CBH I cellulase further comprises a deletion at a position corresponding to T445 in CBH I from Hypocrea jecorina (SEQ ID NO: 2). In a second aspect of this embodiment the variant CBH I cellulase further comprises the deletion of residues corresponding to residues 382-393 in CBH I of Hypocrea jecorina (SEQ ID NO: 2).

In a third embodiment the invention is directed to a variant CBH I cellulase, wherein said variant comprises a substitution at a position corresponding to a residue selected from the group consisting of S8P, N49S, A68T, A77D, N89D, S92T, S113(N/D), L225F, P227(A/L/T), D249K, T255P, D257E, S279N, L288F, E295K, S297T, A299E, N301K, T332(K/Y/H), F338Y, T356L, V393G, G430F in CBH I from Hypocrea jecorina (SEQ ID NO: 2).

In an fifth embodiment the invention is directed to a vector comprising a nucleic acid encoding a variant CBH I. In another aspect there is a construct comprising the nucleic acid of encoding the variant CBH I operably linked to a regulatory sequence.

In a sixth embodiment the invention is directed to a host cell transformed with the vector comprising a nucleic acid encoding a CBH I variant.

In a seventh embodiment the invention is directed to a method of producing a CBH I variant comprising the steps of:
(a) culturing a host cell transformed with the vector comprising a nucleic acid encoding a CBH I variant in a suitable culture medium under suitable conditions to produce CBH I variant;
(b) obtaining said produced CBH I variant.

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